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<h1 id="01%E7%AC%AC1%E7%AB%A0-%E5%AE%9E%E8%AE%AD%E7%BB%83%E4%B9%A0">01第1章 实训练习</h1>
<h2 id="%E5%AE%9E%E8%AE%AD%E7%9B%AE%E7%9A%84">实训目的</h2>
<ol>
<li>熟悉Node.js模块文件编辑与导出使用。</li>
<li>熟悉Node.js模块加载规则。</li>
</ol>
<h2 id="%E5%AE%9E%E8%AE%AD%E5%86%85%E5%AE%B9">实训内容</h2>
<ol>
<li>
<p>Node.js模块导出导入练习。
(1) 创建a.js，代码如下所示。</p>
<pre class="hljs"><code><div> <span class="hljs-comment">//模块内部定义变量</span>
  <span class="hljs-keyword">let</span> version = <span class="hljs-number">1.0</span>;
  <span class="hljs-comment">//在模块内部定义方法</span>
  <span class="hljs-keyword">const</span> sayHi = <span class="hljs-function"><span class="hljs-params">name</span> =&gt;</span> <span class="hljs-string">`您好，<span class="hljs-subst">${name}</span>`</span>;
  <span class="hljs-comment">//向模块外部导出数据</span>
  <span class="hljs-built_in">module</span>.exports={<span class="hljs-attr">ver</span>:version, <span class="hljs-attr">say</span>:sayHi};
</div></code></pre>
<p>(2) 创建b.js，输出a.js中的version信息；调用sayHi方法，输出自定义信息。</p>
<p>参考：</p>
<pre class="hljs"><code><div><span class="hljs-comment">//b.js</span>
<span class="hljs-comment">//在b.js模块中导入模块a</span>
<span class="hljs-keyword">let</span> a = <span class="hljs-built_in">require</span>(<span class="hljs-string">'./a'</span>);
<span class="hljs-comment">//输出a模块中的version变量</span>
<span class="hljs-built_in">console</span>.log(a.ver);
<span class="hljs-comment">//调用a模块中的sayHi方法 并输出其返回值</span>
<span class="hljs-built_in">console</span>.log(a.say(<span class="hljs-string">'柠檬不酸'</span>));
</div></code></pre>
<p>运行：在vscode用<code>ctrl+~</code>打开终端，在b.js所在目录下，执行<code>node b.js</code>。</p>
<p>(3) 小结：Node.js模块如何向外暴露对象？如何加载Node.js模块？</p>
</li>
<li>
<p>Node.js的模块中，exports是module.exports的别名（地址引用关系），导出对象最终以 module.exports 为准。如果要对外暴露属性或方法，就用 exports 就行，要暴露对象(类似class，包含了很多属性和方法)，就用 module.exports。</p>
<p>(1) 新建.js文件，代码如下，查看语句的输出结果：</p>
<pre class="hljs"><code><div><span class="hljs-built_in">console</span>.log(exports===<span class="hljs-built_in">module</span>.exports)
</div></code></pre>
<p>(2) 可以直接在 exports 对象上添加方法，表示对外输出的接口，如同在module.exports上添加一样。注意，不能直接将exports指向一个值，因为这样等于切断了exports与module.exports的联系。同理，给 module.exports 重新赋值也会断开。最后返回的是module.exports。观察如下代码，分析代码的输出结果。</p>
<pre class="hljs"><code><div><span class="hljs-comment">//c.js</span>
<span class="hljs-built_in">module</span>.exports.foo = <span class="hljs-string">'bar'</span>
exports.a = <span class="hljs-string">'abc'</span>
exports = {}  <span class="hljs-comment">//断开连接后，就没联系了，需重新联系起来</span>
<span class="hljs-built_in">console</span>.log(exports,<span class="hljs-built_in">module</span>.exports)
exports.b = <span class="hljs-string">'123'</span>
<span class="hljs-built_in">console</span>.log(exports, <span class="hljs-built_in">module</span>.exports)
exports = <span class="hljs-built_in">module</span>.exports
exports.foo = <span class="hljs-string">'haha'</span>
<span class="hljs-built_in">module</span>.exports.a = <span class="hljs-string">'cba'</span> 
<span class="hljs-built_in">console</span>.log(exports, <span class="hljs-built_in">module</span>.exports)
</div></code></pre>
<p>(3) 小结：exports与module.exports有什么关系？</p>
</li>
<li>
<p>熟悉Node.js模块加载规则。
(1)  在当前文件夹下建立目录&quot;modules&quot;，在该目录内建立模块文件caculator.js，代码如下图所示，理解代码含义。</p>
<img src="02第1章 实训练习.assets/image-20200924164343005.png" alt="image-20200924164343005" style="zoom: 67%;" />
<p>(2) 引用calculator.js方法1：在当前目录下建立<code>test3.js</code>文件，导入上述caculator.js，并调用其中add和subtract函数，输出两数相加及相减的结果。test3.js文件参考代码如下图所示。</p>
<img src="02第1章 实训练习.assets/image-20200924170359703.png" alt="image-20200924170359703" style="zoom:67%;" />
<p>(3) 引用calculator.js方法2：通过配置文件<code>package.json</code>中的<code>main</code>属性指定引用模块，但要注意<code>package.json</code>的存放位置。</p>
<ul>
<li>在当前目录下新建<code>test3_2.js</code>，其代码如下图所示，要求理解代码含义。特别注意第1行，导入模块只是指出了目录，而且路径”./“不能省略。</li>
</ul>
<img src="02第1章 实训练习.assets/image-20200924183442351.png" alt="image-20200924183442351" style="zoom: 67%;" />
<ul>
<li>
<p>在moddules目录中建立配置文件package.json，在其中main属性指定依赖文件。操作时先用命令把modules改变成当前目录，再命令执行如下命令生成配置文件package.json。要注意package.json文件的位置，它位于modules目录中，是为配置modules目录服务的。</p>
<pre class="hljs"><code><div>npm init -y
</div></code></pre>
<img src="02第1章 实训练习.assets/image-20200924184555531.png" alt="image-20200924184555531" style="zoom:67%;" />
<p>在package.json中修改main属性后，配置如下所示。</p>
<pre class="hljs"><code><div>{
  &quot;name&quot;: &quot;modules&quot;,
  &quot;version&quot;: &quot;1.0.0&quot;,
  &quot;description&quot;: &quot;&quot;,
  &quot;main&quot;: &quot;calculator.js&quot;,
  &quot;scripts&quot;: {
    &quot;test&quot;: &quot;echo \&quot;Error: no test specified\&quot; &amp;&amp; exit 1&quot;
  },
  &quot;keywords&quot;: [],
  &quot;author&quot;: &quot;&quot;,
  &quot;license&quot;: &quot;ISC&quot;
}
</div></code></pre>
<p>用命令回到当前目录，并执行<code>test3_2.js</code>。</p>
<pre class="hljs"><code><div>cd..
node .\test3_2.js
</div></code></pre>
<p>(4) 如果将<code>modules</code>目录下的calculator.js文件内容复制到同目录下的index.js文件中，然后更改calculator.js文件名，让package.json中main属性所指的依赖文件不存在。此种情形下执行test3_2.js，是否能正常进行，请试一试。</p>
<p>(5) 小结：</p>
<ul>
<li>const calculator = require(&quot;./modules/calculator.js&quot;)  最常见的方式</li>
<li>如果require(‘./xxx’)指定的是目录，该目录下的package.json中main属性指定了依赖文件，若依赖文件不存在，则会找同目录下的index.js文件。</li>
</ul>
</li>
</ul>
</li>
</ol>

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